Endovascular therapy has been used to treat a variety of different conditions, including control of internal bleeding, occlusion of blood supply to tumors, and relief of vessel wall pressure in the region of an aneurysm. Such therapeutic treatments typically require the use of a catheter to place various treatment materials, devices, and drugs at remote locations within the body. Microcatheters, such as those shown by Engleson, "Catheter Guidewire", U.S. Pat. No. 4,884,579 and as described in Engleson, "Catheter for Guidewire Tracking", U.S. Pat. No. 4,739,768, allow navigation through the body's tortuous vasculature to access such remote sites as the liver or the cerebral arteries of the brain.
For certain maladies, such as vascular malformations and aneurysms, it may be required to create an endovascular occlusion at the defect site. A catheter is typically used to place a vaso-occlusive device or agent within the vasculature of the body to either block the flow of blood through a vessel making up that portion of the vasculature by forming an embolus or by forming such an embolus within an aneurysm stemming from the vessel. In the case of an aneurysm in a parent vessel or artery, for example, the distal end of a delivery catheter is placed within the aneurysm and a suitable vaso-occlusion material or device is delivered through the distal end of the catheter and into the aneurysm, thus forming the desired embolus.
Formation of the embolus may involve the injection of a fluid embolic agent such as microfibrillar collagen, Silastic beads, or polymeric resins such as cyanoacrylate. Ideally, the embolizing agent adapts itself to the irregular shape of the internal walls of the malformation or aneurysm. One risk with this procedure is inadvertent embolism in the parent artery due to the inability to contain the fluid agent within the aneurysm. This is especially true when the opening to the aneurysm is relatively large.
Mechanical vaso-occlusive devices are also well known. One widely used vaso-occlusive device is a wire coil or braid which can be introduced through a delivery catheter in a stretched linear form and which assumes an irregular shape upon discharge of the device from the end of the catheter to engage and fill an opening such as an aneurysm.
For instance, U.S. Pat. No. 4,994,069 to Ritchart et al., shows a flexible, preferably coiled, wire for use in a small vessel vaso-occlusion. Ritchart teaches a coil which is fairly soft that may be delivered to the site using a catheter and pusher. The catheter may be guided to the site through the use of a guidewire (see U.S. Pat. No. 4,884,579) or by flow-directed means such as a balloon placed at the distal end of the catheter. Once the site has been reached, the catheter lumen is cleared by removing the guidewire (if a guidewire has been used), and one or more coils are placed into the proximal open end of the catheter and advanced through the catheter with a pusher. The pusher is typically a wire having a distal end adapted to engage and push the coil through the catheter lumen as the pusher itself is advanced through the catheter. Once the coil reaches the distal end of the catheter, it is discharged from the catheter by the pusher into the vascular site.
The Ritchart et al. coils are typically pushed into the desired vascular site in a linear configuration. Upon discharge from the catheter, the coil may undertake any of a number of random or regular configurations designed to fill the site. The coils are relatively permanent, can be easily imaged radiographically, and may be retrieved.
In addition to using a pusher as described in Ritchart, the vaso-occlusive coils may be discharged from the catheter in a variety of other ways. U.S. Pat. Nos. 5,354,295 and 5,122,136, both to Guglielmi et al., describe an electrolytically detachable embolic device. U.S. Pat. No. 5,234,437, to Sepetka, shows a method of unscrewing a helically wound coil from a pusher having interlocking surfaces. U.S. Pat. No. 5,250,071, to Palermo, shows an embolic coil assembly using interlocking clasps mounted both on the pusher and on the embolic coil. U.S. Pat. No. 5,261,916, to Engelson, shows a detachable pusher-vaso-occlusive coil assembly having an interlocking ball and keyway-type coupling. U.S. Pat. No. 5,304,195, to Twyford et al., shows a pusher-vaso-occlusive coil assembly having an affixed, proximately extending wire carrying a ball on its proximal end and a pusher having a similar end. The two ends are interlocked and disengage when expelled from the distal tip of the catheter. U.S. Pat. No. 5,312,415, to Palermo, also shows a method for discharging numerous coils from a single pusher by use of a guidewire which has a section capable of interconnecting with the interior of the helically wound coil. U.S. Pat. No. 5,350,397, to Palermo et al., shows a pusher having a throat at its distal end and a pusher through its axis. The pusher sheath will hold onto the end of an embolic coil and will then be released upon pushing the axially placed pusher wire against the member found on the proximal end of the vaso-occlusive coil. Finally, U.S. Pat. No. 5,669,931 shows hydraulic discharge of embolic coils. In a preferred embodiment, the coils are provided in an introducer cartridge.
Regardless of the manner of discharge, many embolic coils are subject to the same placement risk as that of fluid embolic agents. That is, as the length of coil is discharged from the distal end of the catheter into an aneurysm, for example, it is difficult to ensure that the coil is contained within the open space of the aneurysm. For example, the distal end or an intermediate section of the discharged coil may be deflected or routed back through the opening to the aneurysm as the coil proceeds to conform to and fill the open space within the aneurysm.
There is a need for a delivery system which overcomes the limitations described above. More specifically, there is a need for a catheter for delivering vaso-occlusive materials or devices which can control the placement of the materials or devices upon discharge from the catheter. The delivery catheter must have a small diameter and have a highly flexible construction which permits movement along a small-diameter, tortuous vessel path.